One-step Conversion Of Unsaturated Fatty Acids To Long-chain N-alkanes And Aromatics Without An Added Hydrogen Donor

With the depletion of fossil resources,growing consumption of aviation fuel and the problem of greenhouse,the development of bio-aviation fuel has attracted great attention.Nowadays,the main technology for producing aviation biofuel is the hydrodeoxygenation of refined vegetable oils,but the high raw material cost and hydrogen consumption hinder its applications.The technology pathway,low-grade greases was hydrolyzed and then decarboxylated/decarbonylated to prepare aviation biofuel,has gained tremendously attention recently.However,the decarboxylation/decarbonylation rates of unsaturated fatty acids/esters are slow,and lack of the important components,aromatics,in the obtained aviation fuel.In this dissertation,the reaction rule and mechanism of the in-situ hydrogen transfer,decarboxylation/decarbonylation and aromatization of oleic acid were systematicly studied.Then the effect of solvents on the catalytic conversion of oleic acid was investigated.A method that Pt/C catalyzes the oleic acid by decarboxylation/decarbonylation and aromatization with the condition of non-solvent and non-hydrogen is established.The method was further applied on the conversion of triglycerides,microalgae oils,waste cooking oils and their hydrolysates.The results showed that this method was suitable for model compounds and raw materials.The main contents are generalized as follows:Firstly,the effects of both catalyst and oleic acid loading on the in-situ hydrogen transfer,decarboxylation/decarbonylation and aromatization of oleic acid over Pt/C were investigated.The product distributions with reaction time at different reaction temperature were performed and then a reasonable reaction pathway was proposed.The reaction pathway was further proved by the reaction behaviors of stearic acid and 1-heptadecene with the same reaction condition.The conversion results of 3-octenoic acid,3-nonenoic acid and oleic acid were compared.The results indicated that 71%yield of heptadecane was achieved after 80 min at 350?.Moreover,19%yield of aromatics,which is the critical component of the aviation fuel,was obtained.The main reaction mechanism was proposed as follows:At first,oleic acid was decarboxylated to 8-heptadecene,followed by the dehydrogenation of 8-heptadecene to polyenes.Then polyenes were cyclized to aromatics by intramolecular Diels-Alder reaction,which provided hydrogen to saturate the unreacted oleic acid to stearic acid.Finally,stearic acid was decarboxylated/decarbonylated to heptadecane.Secondly,three solvent systems(solvent-free,water and dodecane)were employed on the conversion of oleic acid over Pt/C.The effects of solvent loading,catalyst loading and reaction time on the reactions were investigated.The different reaction behaviors of 1-heptadecene and oleic acid with different solvents were compared.The stability and reuse performance of Pt/C in the three reaction systems were also investigated.Finally,the influence ways of solvents on the catalytic conversion of oleic acid were deduced.The results indicated that in the reaction system with dodecane and high temperature liquid water(HTLW)as solvent,the decarboxylation/decarbonylation and aromatization were inhibited.Compared with dodecane,HTLW showed worse decarboxylation/decarbonylation and aromatization performance.The competition of Pt/C active sites by solvents was one of the reasons for the lower yields of heptadecane and aromatics.The water has another impact way for the conversion of oleic acid,which is the H+ released from water and hydrogen bonding existed between water and oleic acid to hinder the decarboxylation/decarbonylation and aromatization.The ICP-MS and TGA results indicated that it was the coke rather than the leaching of Pt/C that leaded to the reduction of catalytic activity in three solvent systems.Recovered Pt/C showed good catalytic activity after calcining at 200?for 2 h.At last,catalytic conversion of triglycerides and oleic acid over Pt/C were measured.Thereafter,microalgae oils,waste cooking oils and their hydrolysates products were chosen as reactants,and the compositions of reactants were analyzed.The product distribution,elemental compositions were studied,and the calorific values of the final products were calculated.The results indicated that the ester model compounds could be reacted as oleic acid,but the reaction rate decreased slightly because of the ester groups.After the reaction,the oxygen content of lipids reduced and the calorific value of products slumped.The microalgae oils and waste cooking oils hydrolysate were reacted at 350?for 80 min,only 3.5%and 1.7%oxygen contents were discovered.Microalgae oils,waste cooking oils and their hydrolysates produced 72%and 31%aviation biofuels,with 45.5 MJ/kg and 48.4 MJ/kg calorific values respectively,the reaction results of microalgae oils and waste cooking oils were similar with their corresponding hydrolysates.Reaction system of solvent-free and hydrogen-free over Pt/C is suitable for the preparation of long-chain alkanes and aromatic hydrocarbons with a suitable proportion by one-step reaction.